1. Field of the Invention
The present invention relates to a lithographic apparatus and, in particular, to wireless signaling for a lithographic apparatus.
2. Description of the Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning devices, such as a mask, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising part of, one or several dies) on a substrate (e.g. a silicon wafer) that has a layer of radiation-sensitive material (resist).
In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the projection beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction.
In a scanner, portions of the substrate are scanned successively. In between a scanning of a portion and a scanning of a next portion of the substrate, a movement is made to position the substrate and the patterned beam relative to each other such that scanning of the next portion of the substrate can start. The scanning movement can be performed by moving the substrate, or by moving a suitable part of the illumination system and/or a suitable part of the projection system.
Moreover, it is possible that each of these elements or any suitable combination thereof is moved thus achieving a desired scanning of the patterned beam relative to the substrate. Also, any other mechanism for moving the patterned beam relative to the substrate can be applied, e.g. making use of electrical optical components.
To achieve an accurate exposure dose or exposure of a target portion of the substrate and avoid variations in the exposure of the target portion (or parts thereof), conventional lithographic systems have to wait until fluctuations in scanning speed settles down and the scanning speed achieves a constant value. Such fluctuations in scanning speed occur in between successive scanning phases, where components have to accelerated and decelerated in order to move the substrate and the patterned beam relative to each other.
As such, to avoid the variations in irradiation due to scanning speed fluctuations, the exposure can only begin after the scanning speed of the patterned beam (should it be irradiated onto the substrate at that moment) relative to the substrate has achieved the desired constant value. As a result, the scanning process is burdened as the scanning speed has to stabilize to a desired value each time a successive target portion is exposed.